Variable sweep hydrofoil



Dec. 22, 1964 E. H. HANDLER 3,

VARIABLE SWEEP HYDROFOIL Filed Feb. 28, 1963 2 Sheets-Sheet 1 INVENTOREugene h. Hand/er AGENT Dec. 22, 1964 E. H. HANDLER 3,162,166

VARIABLE SWEEP HYDROFOIL.

Filed Feb. 28, 1963 2 Sheets-Sheet 2 PUMP United States Patent Ofi3,162,166 Patented Dec. 22, 1964 3,162,166 VARIABLE SWEEP HYDRUFGILEugene H. Handler, Keusington, Mi, assignor to the United States ofAmerica as represented by the Secretary of the Navy Filed Feb. 28, 1963,Ser. No. 261,910

' 3 Claims. (Cl. 114-665) (Granted under Title 35, US. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention pertains generally to a hydrofoil system for supporting awater-borne craft and in particular the invention relates to avariable-sweep hydrofoil by which an appropriate angle of sweep-back,aspect ratio and foil section may be selected as a function of speed.

A hydrofoil is a surface provided below the hull of a water-borne craftwhich provides an upward force component of lift when the craft hasforward velocity with respect to the water. The lift exerted on thehydrofoil by the water is suilicient to raise the hull of the craftabove the surface of the water when the velocity of the craft is ofproper magnitude.

It is well known in the design of high speed boats that the performanceof such craft can be greatly improved by the use of hydrofoils. Manyhydrofoil craft in the past, however, exhibited certain disadvantages.The prior art foil systems are often quite complex; in one common type,for example, each foil support has thereon three or four foils ingenerally vertical alignment. Such an array is heavy, expensive and mayrequire extensive maintenance. In addition, the low speed resistance ofchevron and/ or ladder systems are excessive since both low and highspeed foils are immersed. Furthermore, if the latter havesuper-cavitating sections, their resistance will be extremely high.Additionally, during high speed operation when utilizing the ladder typearrangement of foil support, theuppermost or low speed foils are clearof the water, thus being carried along as dead weight. Also, both thelarge foils and the series of generally vertically supported foilspresent problems of storage when the ship is in port.

The present invention obviates the aforementioned disadvantages byproviding a craft with variable sweep foils. The under side of the hullis provided with symmetrically spaced support struts, the lower ends ofwhich rotatably mount the foils of the instant invention. The foils arealigned with the minimum chord fore-and-aft for the low speed phase ofthe acceleration run or low speed cruise. In this configuration, thefoil has maximum aspect ratio, a term which may be defined as the ratioof span to average chord. In addition, the low speed position isspecifically designed to have a sub-cavitating cross-section.

As the hydrofoil boat speed is increasedfthe foil is rotated to aposition giving the desired chord/thickness ratio and sweep. The angleof rotation in the simplest case is 90, giving maximum aspect ratio andchord/thickness ratio for low speed and minimum aspect ratio andchord/thickness for high speed.

Therefore, objects and features of this invention are the provision ofhydrofoil systems for water-borne craft in which foil configuration maybe optimized for any desired speed within the crafts capabilities.

- provision of a novelhydrofoil system by means of which Further objectsand features of this invention are the smooth transition from low speedto high speed is achieved.

Further objects and features of the invention include the provision of ahydrofoil system having rotatable foils, the variable configuration ofwhich eliminates force and moment discontinuities due to the onset of,cavitation.

Additional objects and features of this invention are the provision ofstructural arrangements for hydrofoil craft of such nature and characteras to minimize weight due to the minimization of foil surfaces and thesimpli fication of design and associated equipment.

Other objects and features and many of the attendant advantages of thisinvention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a side view of the craft in motion illustrating the elevationof the hull above the Water surface and further illustrating the foilsof the instant invention rotated to the high speed position;

FIG. 2 is a top plan view of the craft in FIG. 1, illustrating thesymmetrical paths of rotation of the variable sweep foils of the instantinvention from the high speed position through 90 to the low speedposition;

FIG. 3 is a front elevation view of the craft of FIG. 1;

FIG. 4 is a sectional view with parts broken away of a rotatable foiland actuating mechanism therefor taken substantially along the line 44of FIG. 2; FIG. 5 is a transverse sectional view with parts broken awayof the foil, the foil supporting strut and the rotation actuationmechanism taken substantially along the line 5-5 of FIG. 4;

FIG. 6 is a top plan view of a typical foil showing the generalconfiguration thereof;

FIG. 7 is a sectional view of a foil taken substantially along the line7-7 of FIG. 2 in which the cross-section of the foil is optimized forlow speed with regard to water flow past the foil from right to left;

FIG. 8 is a sectional view of the foil taken substantially along theline 8-8 of FIG. 3 in which the cross-section of the foil is optimizedfor high speed with regard to fiow of water past the foil from right toleft; and FIG. 9 is a view similar to FIG. 7 of a typical aft foilshowing the optional reduced-thickness, cross-sectional configuration.

Referring now to the drawings and in particular to FIGS. 1, 2 and 3, anembodiment of the hydrofoil system of the invention is shown mounted ona generally con-v ventional boat 10 having a hull 12 driven by apropeller 14, which propeller is mounted on shaft 16 connected to asuitable source of power (not shown). Directional control of thecraft ismaintained by manipulation of rudder 18 in the conventional manner.

In accordance with this invention the hydrofoil system comprises a pairof forward hydrofoils 2t), 22 and a pair of aft hydrofoils '24, 26rotatably mounted on supporting struts Z1, 23, 25 and 27-, respectively,which are secured to boat hull 12. These supporting struts areconstructed in the general form of an airfoil in order that dragresistance may be reduced to a minimum. As may be seen in FIG. 3 thefoils are secured to the craftvat an angle of sufficient dihedral topromote stability.

FIGS. 4 and 5 illustrate a representative mechanism suitable forimparting rotational movement to said foils about the ends of thesupporting struts. A typical foil;

supporting strut, member 23 comprises a primary load carrying frame 30enclosed by a foil shaped housing 31. Frame 30 is a hollow structureterminating-in a stepped bore for bearing surface32 and an outwardlyextending flange 33. An upwardly extending column 34 issecured to theupper surface of the foil and is received within'the hollow frame 30.The column is provided adjacent the opposite directions.

foil with. a bearing surface 35 of such dimensions as to rotatablyengage the lower stepped bore bearing surface 32 of saidframe.Appropriate seals 32a as, for example, O-rings are provided between thebearing surfaces in order to exclude ambient sea water from within frame39. Column 34 may be further axially supported within. the frame 30 atits upper end 38 by sleeve 39 concentrically arranged within frame 3thThe upper surface of the foil is further provided with an annular collar36 concentrically positioned about column 34. Frame flange 33 'isslidably retained within said collar thereby retaining the foil inrotative sliding abutment with the end of the strut support frame. Foil22 is therefore retained in freely rotatable condition on the end .offrame 36 in both radial and axial directions by column 34 and theabutting association of flange 33 with collar 35. v.

Rotative motion may be imparted to the foil by any one of a number ofinstrumentalities. One such system is shown in FIGS. 4 and 5. Aninternal ring gear 42 is secured to the top of column 34 by bolts 43 andis engaged and driven by pinion 44. The pinion may be powered by anysuitable means as, for example, a hydraulic motor 45 convenientlylocated within frame 39. The pump for the motor and necessary controlsfor directing foil movement are conveniently placed within the boat andmay be driven by means of a power take-off from the boat power plant. Inorder that the foils may be maintained inany desired position,instrumentalities such as an accumulator, pump bypass and holdingvalves, or a mechanical one-way drive gear system may be used. Inaddition, the pump is reversible to accommodate bidirectional operationof the foils.

become apparent to those skilled in the art. Ring gear 42 is provided onits exterior surface with an abutment 46 which is engageable with eitherof two blocks 47 mounted within frame 30, thus limiting rotation of thering gear, column and foil to 90 for purposes disclosed hereinafter.Housing 31 is provided with a removable panel or door 48 for access tothe foil rotation mechanism located therewithin.

Referring now to FIGS. 2, 6, 7 and 8, the hydrofoils of the instantinvention are rotatable about their supporting struts from positionshaving transverse axis AA through 90 to positions having transverse axisBB. In this manner, a single foil may be provided with a configurationwith regard to one axis which is optimized for low speed and, inaddition, a configuration along an other axis beneficial for high speed.To this end the foils of the instant case are formed with asub-cavitating crosssection, FIG. '7, having. minimum chord fore-andaftfor the low speed phase of the acceleration run or low speed 'eruise-This low speed configuration, having transverse axis A'A, is illustratedin FIG. 2n the dotted lines. In this position, the foil has maximumaspect ratio as well as 'chord/ thickness ratio, both of which aredesirable featuresfor achieving the optimum relationship of lift toresistance at low speeds. V V

As the hydrofoil'boatspeed is increased, the foil :may be rotatedthrough a sequence of positions in order'that i the desired sweep andchord/thickness ratiomay be ob tained. When top speed is reached thefoil has been rotated through 90 thereby presenting a foilconfigurationin which BB isthetransverse axis as shown in FIGS. 1, 2, 3and 6. In this position both the aspect ratio and the chord/thicknessratio have been minimized :a's'shown .in FIG. 8.

In order to maintain 'symmetry' and to stabilize the motion of the boat,opposing pairs of foils are rotated in FIG. 2 illustrates the preferredinward [rotation of foils 26 and 22 from high speed positionstothoselocations better adapted for lowspeeds.

Rotation from. low speed to high speed positions is achieved in-tlieopposite manner, foil 20 being rotated Numerous alternatives forachieving desired foil rotation may be used as will outwardlycounter-clockwise and foil 22 being rotated outwardly clockwise to theposition shown in FIG. 2.

Aft foils 24 and 26 may be of similar configuration to, and may berotated in a similar manner as, their forward counterparts. It may bedesirable, however, to provide the aft foils with a configuration ofreduced thickness, shown in FIG. 9, so as to delay separation of flowand the consequent deterioration in stability. Although the directionsof rotation of the aft foils are identical to those of the forwardfoils, the need for rotation may be decreased or eliminated if the aftfoils are used primarily for longitudinal stabilization. In this use theonset of cavitation would not seriously affect the aft foils left whichhas been minimized in accordance with their function as stabilizers.

In operation, with the hull of the boat resting on the surface of thewater prior to acceleration, the hydrofoils are rotated to the positionsshown in dotted lines in FIG. 2 having minimum chord fore-and-aft andmaximum aspect ratio. As the craft accelerates, the foils are rotatedoutwardly in order that the optimum lift/resistance relationship may bemaintained by permitting an appropriate angle of sweep-back, aspectratio and foil section to be selected as a function of speed. As thecraft obtains top speed, at which the hull is supported above thesurface of the water by the foils, the foils will be rotated to thosepositions shown in FIG. 2 wherein the chord fore-and-aft is maximized,resulting in minimum aspect ratio and chord/ thickness ratio.

It will be apparent from the foregoing description that the provision ofvariable sweep hydrofoils for a waterborne craft in the manner taughtherein achieves the objectives of optimizing foil configuration for anydesired speed within the capabilities of the craft. Another benefit ofthe instant invention is realized in economics of initial cost,maintenance and weight by virtue of the simplifiedsystem and thedecrease in number of foil surfaces over those required in the priorart. A further advantage is the elimination of force and momentdiscontinuities due to the onset of cavitation as well as a smoothtransition from low to high speed.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. For example, the angleof rotation from low speed alignment to high speed alignment forpurposes of illustration was chosen to be However, optimum foilalignment in any given specific situation may define an angle ofrotation of different magnitude than 90. Optimum angle determinationwould be dependent upon foil shape, size and attitude, as well as thecraft velocity and the properties of the fluid, e.g., fresh water orsalt water. The precise plan view of the foils depends upon the sectionschosen for it; that is, for example, whether the cross-section issub-cavitating or super-cavitating, and whether the foils are to be usedfor longitudinal stabilization.

It is therefore to be understood that within the scope of the appendedclaims the invention may be practiced otherwise than as specificallydescribed.

What is claimed is:

1. A waterborne craft comprising a hull,

a hydrofoil system including at least a pair of symmetrically locatedhydrofoil supports extending generally downwardly from said hull,

variable sweep hydrofoils, each hydrofoil having a foilshapedcross-scetionabout each of two substantially v perpendicular axes,continuously immersed during operation and rotatably secured to saidsupports,

-, said hydrofoils having effective aspect and chord/ thickness 'ratioswhich vary as a function of the angle of sweep of said hydrofoils,

I control means in said craft operatively connected to said hydrofoilstoset the foils to any selected intermediate sweep angle between twopredetermined limits,

thereby to provide at any given speed within the speed range of thecraft a hydrofoil sweep angle which optimizes the lift/resistance ratiofor that particular speed. 2. In the craft according to claim 1, saidhydrofoil system comprising pairs of hydrofoils and supporting strutslongitudinally spaced along said craft, the aft hydrofoils being thinnerthan the forward hydrofoils whereby separation of flow may be delayedthereby maintaining stability of operation of the hydrofoil system. 3.The craft according to claim 2 wherein said pairs of hydrofoils andstruts comprise one hydrofoil positioned on the starboard side of saidcraft and the other hydrofoil symmetrically located on the port side ofsaid craft and References Cited by the Examiner UNITED STATES PATENTSDawson 244105 Barkla 114-665 Wendel 114-665 Follett 114--66.5 Headricket a1 114--66.5 Smith 11466.5

15 FERGUS s. MIDDLETON, Primary Examiner.

1. A WATERBORNE CRAFT COMPRISING A HULL, A HYDROFOIL SYSTEM INCLUDING ATLEAST A PAIR OF SYMMETRICALLY LOCATED HYDROFOIL SUPPORTS EXTENDINGGENERALLY DOWNWARDLY FROM SAID HULL, VARIABLE SWEEP HYDROFOILS, EACHHYDROFOIL HAVING A FOILSHAPED CROSS-SECTION ABOUT EACH OF TWOSUBSTANTIALLY PERPENDICULAR AXES, CONTINUOUSLY IMMERSED DURING OPERATIONAND ROTATABLY SECURED TO SAID SUPPORTS, SAID HYDROFOILS HAVING EFFECTIVEASPECT AND CHORD/ THICKNESS RATIOS WHICH VARY AS A FUNCTION OF THE ANGLEOF SWEEP OF SAID HYDROFOILS, CONTROL MEANS IN SAID CRAFT OPERATIVELYCONNECTED TO SAID HYDROFOILS TO SET THE FOILS TO ANY SELECTEDINTERMEDIATE SWEEP ANGLE BETWEEN TWO PREDETERMINED LIMITS, THEREBY TOPROVIDE AT ANY GIVEN SPEED WITHIN THE SPEED RANGE OF THE CRAFT AHYDROFOIL SWEEP ANGLE WHICH OPTIMIZES THE LIFT/RESISTANCE RATIO FOR THATPARTICULAR SPEED.